Roasting gives the coffee its aroma and taste
Today we look at the alchemy of coffee, the process that makes it a miracle for our nose and tongue. For centuries, people have been trying new tricks and mysterious recommendations to extract even more treasures from the bean, to increase the value of their coffee and attract more customers.
Roastery
The structure houses a perforated drum that has vanes inside and is connected to the motor. There are gas burners under the drum (approx. 10 cm below the drum) and a cyclone with a motor is connected to the drum. During roasting, the drum rotates and stirs the coffee (about 50 times per minute), under which a fire burns from burners whose intensity is controlled by the roaster. The cyclone pulls this hot air produced by the burners through the drum. So the coffee is roasted primarily by touching the hot drum (conduction 70%), and secondarily by the hot air passing through it (convection 30%).
Green, i.e. raw coffee = almost no taste.
In modern times, the roasting process is controlled by computers. Nevertheless, man is still irreplaceable in this process. During the entire roasting process, the roaster guards the coffee, selects samples and, as necessary, adjusts the temperature, amount of air, speed of rotation of the drum and length of roasting.
Large roasters that produce huge amounts of coffee and roast in large roasters leave this entire process to computer technology alone. But it's like a barista working with a fully automatic coffee machine. The coffee machine does all the work for him, but the resulting product is not of such high quality. For this reason, you should always reach for selected coffee, where you can be sure of freshness and quality.
Stages of roasting
0 min. – start of roasting
1 min. and 30 sec. – drop
2 min. – turn
3 - 6 min. – drying
7 - 9 min. – Maillard reaction and caramelization
10 - 12 min. – 1st crack
12 - 14 min. – grain development
15 min. – end of roasting
16 - 19 min. – 2nd crack (2nd crack)
Chemistry hidden in the grain
VOLATILE AND NON-VOLATILE COMPOUNDS
Volatile compounds are what cause aroma, non-volatile compounds contribute to taste.
Volatile compounds are organic compounds that evaporate at room temperature. When the volatile compounds that create the aroma dissipate, we smell coffee. Volatile compounds include:
Aldehydes that add a fruity, green scent.
Furans that contribute to the typical caramel aroma.
Pyrazines, which contribute to the earthy aroma.
Sulfur-containing compounds including 2-furfurylthiol. Some of them have an aroma that is commonly described as "roasted coffee", but there are also some that don't smell very appealing.
Guaiacol, which has smoky and spicy notes.
Non-permanent compounds are substances that are stable at room temperature. That means they don't evaporate. Some of these compounds change during roasting, while others remain stable during the process.
An example is caffeine, which is responsible for some bitter tastes. Caffeine occurs naturally in coffee and is not changed by the roasting process. Other non-volatile compounds include sucrose, which provides sweetness, and lipids, which create body and the resulting mouthfeel. Melanoidins create color and body.
SIGNIFICANCE OF ACIDS
Acids are very sensitive to heat and roasting can degrade some acids and create others. For example, citric and tartaric acids create fruity and sweet notes that break down during roasting. If you roast the coffee beans for too long and at high temperatures, you will reduce the overall sweetness of the resulting profile. In addition, coffee contains a high amount of chlorogenic acid, which breaks down into caffeic and quinic acids during roasting. They are believed to add bitterness and astringency to coffee.